Abnormal-abdomen is a major gene-multiple modifier gene controlled phenotypic abnormality which results in a loss of abdominal hypoderm and the malformation of tergites and sternites in the adult fly. The mutant genotype is responsible for an increased in vitro aminoacylation of tRNA and an increase in the incorporation of amino acids into protein. The phenocritical period for the action of the mutation is primarily embryonic but also is expressed during late larval development. The observed increase in tRNA aminoacylation involves quantitative rather than qualitative changes in charging. Protein synthesis is increased during pharate adult differentiation, and the increased soluble protein content of adult flies has been shown to involve specific quantitative increases in ten of the twenty-eight separable electrophoretic classes of proteins. The research proposed in this application involves a morphogenetic and molecular investigation of the mutant control mechanisms responsible for the developmental abnormalities of the adult hypoderm. A primary second chromosome enhancer of the major sex-linked gene will be localized; and its effect on the protein synthetic system associated with the residual genotype will be studied. We also expect to study in vivo protein synthesis in both mutant adult flies and in mutant embryos as well as to study in vitro tRNA aminoacylation during embryonic development. The studies are designed to test the hypothesis that increased aminoacylation and protein synthesis during embryonic development is correlated with the effective time of action of the mutant genotype. Histological studies at the levels of the light and electron microscopes will be made in order to examine the gene controlled changes in tergite development at the level of differentiating cells and tissues. We will also begin an investigation of the physical properties of the aminoacylating enzymes and a study of the relationship between protein synthesis and the function of the major gene. BIBLIOGRAPHIC REFERENCES: Shafer, S. Olexa, S., and Hillman, R., 1975. Macromolecular complexes of aminoacyl-tRNA synthetases in Drosophila, Insect Biochem. in press. Olexa, S., and Hillman, R., 1976. Characterization of a complex of aminoacyl-tRNA synthetases in Drosophila melanogaster, Amer. Zool. in press (abstr.)